Casting of metals by means of molds



March 4, 1958 K. PFAFF CASTING 0F METALS BY MEANS OF moms 3 Sheets-Sheet 1 Filed NOV. 5. 1952 'wvE/vr'o/z, KAKL PFAFF'(deceased) BY HAIZTMUTH ZUEDINE-R ADMINISTIQATOR J; /W 4W HIS 196E405 March 4, 1958 PFAFF 2,825106 7 CASTING 0F METALS BY MEANS OF HOLDS Filed Nov. 5.1952 I 3 Sheets-Sheet 2 v v 76 KARL PFAFF(deeased) BY HARTMUTH KUEDWICQER ADMIN/s TRATOR;

March 4, 1958 I K; PFAFF 2,825,106

CASTING OF METALS BY MEANS OF Moms Filed Nov. 5. 1952 s Sheets-Sheet a INVENTOR KARL PFAFF (deceased) BY HARTMUTH RUEDINGEIZ ADMINISTRATOR.

HIS HGENTS.

United States Patent() CASTING OF METALS BY MEANS OF MOLDS Karl Pfatf, deceased, late of Kaiserslautern, Germany, by Hartmuth Riidinger, administrator, Kaiserslautern, Germany, assignor to G. M. Pfalf Aktien-Gesellschaft, a corporation of Germany Application November 5, 1952, Serial No. 318,802

Claims priority, application Germany May 13, 1952 4 Claims. (Cl. 22-129) This invention relates to the casting of metals by means of molds, which in contradistinction to customary thick walled steel molds, have thin walls and therefore are often denoted as shell molds. This denomination, therefore, will be adhered to for the purpose of the following description.

These shell molds are often manufactured by applying to customary molds, pattern plates and models mixtures of sand and hardenable binders, for instance hardenable resins. The models used for the production of the shell molds may be made of metals, gypsum and other suitable materials. These mixtures may be applied to the models or pattern plates by blowing or by any other suitable manner.

It is, however, immaterial for the purposes of this invention how the shell molds are produced; however, the use of the shell mold forming mixtures is preferred in the liquid state. The models or base molds for the production of the shell molds may first be provided with a layer of fat, which facilitates the removal of the finished shell mold. Thereupon the shell mold forming mixture is applied to the models or molds, preferably in the wet state; thereupon the models are covered with dry sand and dried.

The materials used for the production of the shell molds should be selected in such a manner that the finished shell molds adhere to the models by adhesion only. By the transmission of'heat from the generally heated base molds or models to the cold shell mold forming mixtures the binder material contained therein will soften and form on the models a layer of a uniform thickness. Upon removal of non-heated portions of the applied mixture the shell mold forming layer is heat-hardened.

Thereupon two halves of the thus produced shell molds are superposed upon each other after insertion there'- between of the required cores; the mold halves are connected and locked together by clamps orother suitable means. 1

Thereupon the thus produced shell mold is generally embedded in aloose mass of silica, sand or the like materials the shell mold being preferably maintained in the bed forming material in a vertical position. A more detaileddescription does not seem to be required, since the methods of producing these'shell' molds are generally known.

However, the disadvantages and shortcomings of the known shell mold manufacturing processes are manifold and this is the explanation for the greatlyreduced application of these shell molds. j

First of all the resiliency of the above mentioned clamps is gradually reduced by the comparatively high'manufacturing temperature; as a consequence thereof, the clamps must be often replaced. The placement of the clamps, the application of the forming materials and other necessary. working steps require considerable time. The sand or the silica containing materials used in the manufacture of the shell molds often becomes so intimately mixed with'the mold layer forming materials that it cannot be.

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recovered; this is a great disadvantage, since considerable quantities of sand or silica are required as bedding materials. Further shortcomings arise insofar as the compression of the mold halves by the clamps is restricted to the outer portions; in the center portion, the action of the clamps is comparatively poor. Moreover the pres sure exerted onto the bedding material is often too small to maintain the shell mold halves along their junction in the required operative position. Consequently protrusions, ridges and other shape irregularities may be formed along the joints between the mold halves and additional working steps are required to remove the same.

Moreover, it often happens that the shell molds swell during the casting process, which leads to the production of inaccurate castings.

When casting into vertical shell molds the static pressure particularly in the lower part thereof is often so high that the mutual position of the mold halves is changed; consequently irregularly shaped castings result.

As a consequence of these conditions, it is practically impossible to apply the known shell mold casting methods to the production of large objects.

Finally, the workpieces which are cast by means of the embedded shell molds cool-off very quickly due to the heat conductivity of the bedding materials; as a consequence thereof, very often hard castings result.

It is the main object of the invention to eliminate these grave shortcomings and disadvantages of the customary mask mold production methods.

This object is substantially attained by supporting during casting the finishedshell mold halves in a horizontal position upon a plane plate-shaped support and weighting the same from above with a plate having a shape and size substantially similar to that of the shell mold. The weight of this loading plate is controlled in such a manner that the same corresponds to the so-called casting weight which latter denotes the pressure or tension exerted by the metal which is poured into the mold.

A further characteristic element of the invention consists therein, that the upper andlower shell mold halves forming bodies are provided with edge supports. These supports may be shaped as continuous .or interrupted ledges, or they may have a columnar shape. I

The inwardly situated parts of the shell molds may also be reinforced, whereby portions result which have the same height as the supports. In this manner bearing faces are produced where the lower mold half rests on its base, whereas the upper mold half takes up the weight of the loading plate. In this manner the two shell mold halves are during the first phase of the casting procedure sufficiently pressed together to prevent their lifting.

The before mentioned supports carry the weighting load from the moment where atthe start of the casting operation the shell mold stabilizing heat-hardenable binder is burnt off in the parts of the shell mold directly surrounding the shaping space and where only the sand re-' mains, which by itself does not form a support.

As apparent from the above the invention does not require the embedding of the shell molds. Moreover, the clamping together of the mold halves is eliminated.

By the horizontal location of the casting mold accord ing to the invention the static pressure is essentially reduced; as a consequence thereof the surfaces of the cast ings are true to scale, are even and free of ridges; finishing steps are not required. The reduced cooling speed enables the production of softer castings.

In conformity with a further embodiment of the invention, the supports of'the shell' molds are equalized by the provision of a heated plate to create equally high bearing faces for the weighting load and for the support of the lower plate. Y. The heated plate is applied at the moment when the binder and the sand are ap 3 plied to the hot shape-forming parts and the mixture of binder and sand is not completely baked and still in a plastic state.

Further details and characteristics of the invention, as well as the advantages obtained therefrom will be apparent from the following detailed description and the attached drawings showing preferred embodiments thereof, without, however being restricted to the same.

In the drawings.

Figure l is a perspective view, partly in section, of a shell mold constructed in conformity with the invention including its upper loading weight;

Figure 2 is a plan view of the upper shell mold plate or mold half adaptedto be used for the contemporaneous casting of a plurality of machine parts;

Figure 3 is a sectional view on line III to ill of Figure 2;

Figure 4 is a front elevational view of a mold plate or mold half shown in Figure 2;

Figure 5 is a plan view of a further embodiment of the lower mold plate;

Figure 6 is a vertical sectional view on line VI to VI of Figure 5;

Figure 7 is a front elevational view of the mold plate shown in Figure 5;

Figure 8 is a plan view of a further modification of the bottom plate;

Figure 9 is a vertical sectional view on line IX to IX of Figure 8;

Figure 10 is a side elevational view of the bottom mold plate shown in Figure 8 and Figure 11 is a vertical sectional view on line XI to XI of Figure l.

These shell molds produced in conformity with the invention are provided with mold supports located in such a manner that upon assembly of the mold the mold halves are in an accurately superposed tight position. The mold supports are shaped and arranged in conformity with the mold models or the articles. to be cast.

The shell mold shown in Figure 1 consists of an upper half mold or mold plate and a lower mold halve or plate 21.

In conformity with Figures 1 and 2, the upper half of the mask mold has a continuous elevated border support consisting of the circumferential ledge 1. This support is provided with cavities 4, Figure 3, to provide mold cavities.

The mold has holes 2 for the reception of dowling pins 2' Figure 1, connecting the two halves of the shell mold for a proper operating position.

A metal inlet 3, Figures 2, 4, 11, is provided in the upper half of the mask mold. Numerals 4, Figures 2, ll, denote the molding spaces or cavities for the articles to be cast. The lower half 21 of the shell mold is similarly constructed as the upper half 20 with the only exception that the opening 3 for the admission of the casting metal is missing. The lower mold half .21 cooperates by means of its ledge 1 with the upper ledge 1 of the upper mold half 20; the casting cavities of the lower shell mold 1, Figure 11, are denoted with 4.

The general positioning of the two mold plates or mold halves 20, 21 forming the shell mold proper is apparent from the drawings, for instance Figure 11.

The ledge 1 of the upper mold plate 20 contacts the upper cover plate 5, Figures 1, 11; the ledge of the lower mold half or plate is supported on a bottom plate 6-, Figures 1, 11. This bottom plate is provided with grooves 7 and openings 22, Figure 11, which permit the exit of the gases from the closed mold.

Figures 1, l1 illustratethe mountingof the closed mold composed of the upper and lower mold half' or mold plate for actualeasting' purposes. A

A weight plate 10 having handles 9 is located upon the cover plate 5 the latter beingprovided withhandles 8, Figure 1. This plate 10 should preferably have the combined weight of the castings.

A recess 11, Figure 11, provided in plate 5 surrounds the inlet 3 for the molten metal, Figure ll. The inlet 3 may be provided with an upper neck 3', Figure l, which projects through the opening 11 of the cover plate 5, Figures 1, 11.

In conformity with the embodiment of the invention shown in Figures 5, 6 and 7 the continuous supporting ledge 1 is replaced by individual supports 12, which are located along the edge of the shell mold. Similarly to Figures 2-4, the walls of the molding spaces proper are upwardly extended to form supports for the cover plate 5, which supports have an equal height.

The casting spaces are denoted with numerals 13, the inlet for the molten metal by numeral 14 and the doweling pins by numeral 15. The lower mold plate is provided with passages for the molten metal.

With the embodiment of the invention illustrated in Figs. 8, 9 and 10, the continuous supporting ledge 1 of Figs. 2 to 4 and the supports 12 of Figs. 5 to 7 are replaced by columnar supports 16, which are provided at the circumference of the shell mold and between the individual mold cavities l3. Doweling pins 15 connect and position the mold halves.

In conformity with Fig. 9, the columnar supports 16 may be hollow.

The Figs. 8 to 10 show the lower half of the shell mold; the upper half is correspondingly built and provided with an inlet for the molten metal as well as with guide channels for the latter.

The supports for the mold halves or plates maintain their shape during the supply of the metal until the binder applied to the walls of the shell molds and consisting of heat hardenable artificial resins is burnt away by the heat of the molten metal within the range of the parts of the shell mold directly surrounding the casting spaces; when this has happened the castings are sufficiently solidified and stable to act as supports for the loading weight 10, Figs. 1, 11.

Since certain changes in carrying out the above process could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

Having thus described the invention, what I claim as new and desire to be secured by Letters Patent, is as follows:

I claim:

1. A method of casting metals into shell molds baked from a mixture of molding sand and heat hardenable binder comprising horizontally superposing for the supply of the molten metal two shell mold halves upon a flat support, loading said superposed shell mold halves from above with a plate-shaped weight having the tip proximate shape and size of the mold and adjusting the weight of said plate-shaped weight to approximately equal the weight of the cast articles, and creating plane parallel bearing areas for the shell mold halves relative to said flat support and said plate-shaped weight by the provision of equally high columnar supporting members therebetween which improve the bearing capacity of the shell mold halves and take up the stresses exerted upon thesame.

2. A method according to claim 1, comprising producing thesupporting members from the same material mixture. of which the shell molds are made to form the walls of the shell molds and said supporting members into a single homogeneous body.

3 A method according to claim 2, for the production of supports for the plate-shaped weight of an equal height comprising equalizing the supportingqparts of the .shell molds by applying to the shellmolds heated plate-shaped patterns at the moment when the mixture of the heat hardenable binder and the molding sand is still in a plastic state.

4. A shell mold for casting metals comprising two horizontally superposed mold halves made of a mixture of molding sand and heat hardenable binders, a fiat support supporting the lower half and a plate-shaped Weight having the approximate shape and size of the mold supported on the upper half of the mold, each half of the mold including a plurality of equally high hollow columnar supporting bodies uniformly distributed throughout.

References Cited in the file of this patent UNITED STATES PATENTS 342,882 Smith June 1, 1886 6 488,513 Anderson Dec. 20, 1892 2,368,719 Miller Feb. 6, 1945 2,423,151 Miller July 1, 1947 2,449,136 Pattison Sept. 14, 1948 FOREIGN PATENTS 832,934 Germany Mar. 3, 1952 OTHER REFERENCES Modern Metals, April 1952, vol. VIII. No. 3, pages 2340, 32 and 33. (Copyin 22-193 SM.) 

